Automatic control system for aircraft retractable landing gear



.J. H. MILLER Jan. 1, 1952 AUTOMATIC CONTROL SYSTEM FOR AIRCRAFTRETRACTABLE LANDING GEAR Filed Sept. i0, 1948 TI'II JAMES H. MILLER ANW-Illin- Patented Jan. 1, 1952 UNITED STATES PATENT OFFICE AUTOMATICCONTROL SYSTEM FOR AIR- CRAFT RETRACTABLE LANDING GEAR The presentinvention relates to an automatic control system for aircraftretractable landing gear and more particularly to an automatic controlsystem for raising after take-off, and lowering prior to landing,aircraft retractable landing gear.

It is generally well known that a large percentage of aircraft crashesare caused by human error. This is particularly true of crashesresulting from landings wherein the wheels remain in retracted position.The present invention is concerned chiefly with the elimination of thefunction of the pilot in the lowering of the landing gear preparatory tolanding and the concomitant elimination of one form of human error inaircraft travel.'

Briefly, this invention comprises an automatic device mounted in theaircraft and arranged to control the actuating source for raising andlowering the aircraft landing gear. The device comprises motive means,means operable by said motive means for controlling the actuatingsource, relay means for actuating said motive means, and switch meansresponsive to the speed and the inclination of the aircraft forcontrolling the operation of said relay means.

In operation, with the craft flying at a given altitude, at a safeflying speed and with the landing gear in retracted position, the pilotproceeds to prepare for landing by reducing the power and setting thecraft in its angle of descent. As soon as the angle of descent reaches apredetermined degree and the air speed-de creases to a predeterminedvalue, the switch means operates the motive means which causes thelanding gear to be lowered. Upon the takeolf of the craft, the air speedand the angle of climb actuate the motive means in a reverse directioncausing the landing gear to rise.

An object of the present invention is to provide an automatic controlsystem for aircraft retractable landing gear which is responsive to theflight conditions of the craft.

Another object is the provision of an aircraft automatic control systemresponsive to the inclination and the air speed of the craft.

A further object of the invention is the provision of automatic controlmeans for an aircraft for lowering the landing gear of the craft priorto landing and for raising the gear after take-off.

A still further object is to provide automatic .j i

control means for an aircraft for lowering the landing gear of the craftwhen the air speed reaches a predetermined minimum value and theinclination of the craft attains a predetermined angle of negativepitch. y

amended April 30, 1928: 370 O. G. 757) A final object of the presentinvention is the provision of automatic control means for raising thelanding gear of an aircraft when the air speed attains a, predeterminedmaximum value and the inclination of the craft reaches a predetermineddegree in another direction.

Other objects of the invention will hereinafter become more fullyapparent from the following description of the annexed drawings, whichillustrate a preferred embodiment, and wherein:

Fig. l illustrates a side elevation of an aircraft showing the system ofthe present invention mounted thereon.

Fig. 2 is a schematic diagram of the system of Fig. 1 illustrating theposition of the various elements of the system when the aircraft isclimbing after take-olf and the landing gear is in the process ofretracting.

Fig. 3 is a view similar to Fig. 2 showing the elements in landingposition.

Referring now to the drawings, wherein like reference charactersdesignate like or corresponding parts throughout the several views,there is shown in Fig. l an aircraft I I having landing gear I'2 and theautomatic control system I3 mounted thereon. The system I3 may bedirectly connected to the landing gear I2, or, preferably, may beconnected to the actuating source (not shown) for the landing gear andpositioned so as to control the operation of the source, and thereby theoperation of the landing gear.

The system I3, as shown in Fig. 2, comprises a landing gear positionselector I4 connected to the actuating source (not shown) and operableby an electric motor I5, preferably of the reversible type. The motor ispreferably provided with limit stops in its extreme forward and reversepositions wherein the landing gear is either fully retracted orextended.

Motor I5 is controlled by an electromagnetic relay I6 having a coil Iland an armature I8,

the armature I8 carrying a pair of contacts I9A and 2l, one of which, 2|is grounded. Relay I5 has four fixed contacts, interconnected in pairs,one of each pair being connected to motor I5 by means of leads 22 and23, respectively, thereby forming a reversing switch for motor I5.Armature I8 is normally biased to the upper position, as shown in Fig.3, whereby electrical connection is made to the motor in such manner asto maintain the landing gear I2 in extended position. It is to beunderstood that the specific switch connections are merely shown asillustrative and that any other reversing type connection may be used.

Coil I1 or relay I6 has one of its ends connected to one end of a powersupply, such as a battery 24, through limiting resistor 25, and to onecontact 25 of an inclinometer switch 21. Battery 24 has its other endgrounded and has its one end connected yto two other contacts 28, 29 ofswitch 21, the fourth contact 3i of switch 21 being connected to one ofthe xed contacts 32 of air speed switch 33.

Inclinometer switch 21 preferably consists of a glass tube 34 with asmall 'amount of mercury 35 contained therein, the mercury./-electrically connecting the adjacent contacts when it .is in eitherof its extreme positions. "The travel of mercury 35 within tube 311. isgoverned by the off-level position of the tube having .its endsangularly spaced preferably approximately "five degrees from the thrust`line iof .the'f-aircraft. Thus, it is apparent that as the nose ofvthe'vaircraft Il rises, the mercury 35 travels to the rear of the tubeV34 thereby electrically connecting `contacts 26 and .'28, and .thatwith the nose down more than five-degrees the mercury travels .to 'thefront of the tube thereby electrically connecting Vcontacts 29 Vand 3 I.

Air speed switch 33 has a second fixed contact 36 connected to groundand 'also connected to the other end of 4'coil I1 through a limitingresistor 31, while the movable contact 33 of switch 33 is 'connected tothe other end of coil I1. Air speed switch 33 'further comprises an airtight case I59 vented tothe airspeed Venturi tube (static), not shown,the case 33 containing a sensi-tive bellows 4I joined to the air speedPitot tube (pressure), `not shownfa'nd to a main shaft 42 Lto whichthelmovablecontact 38A is connected. All :of the contacts of switch 33are within case 39, movement of contact 38 being controlled by theyexpansion and contraction Vof bellows di. Contacts 32 and 3G areadjustable, onefbeing preferably set in `a kposition which correspondsto asafemargin 4above stalling speed while 'the other is preferablyfixed to Vvcorrespond with va safe margin above -fiying speed.

In operation, the position of theelements shortlyaft'er take-off as Ythecraft II lis climbing is shown in-Fig. 2. The nose of craft I'I hasrisen sufliciently'to cause mercury 35 to move to the rear V-of tube 34thereby connecting contacts 25 and 23, while thespeedof craft II hasexceeded the flying speed so that diaphragm 4I has eX- pandedsufficiently to move shaft 42 -so that contact 38 is connected toContact 36. In this positionV a circuit Yis completed from battery 2d,contacts 26 and 28, coil i1, `contacts '3,5 and 38, to ground, therebyenergizing coil I1 and drawing armature I3 downward to completethevcircuit to motor I whichdrives selector I4 to the retractedposition.

As craft II levels o'if the mercury 35 moves back toward the center' of.glass 34 disconnecting contacts 26 and 28, but the current passingthrough coil I1 from battery 24 and through resistor 25, althoughinsufficient to energize the relay I6, is sufficient to maintain itenergized. If the craft were to nose downward during ight and mercury 35'connected contacts r25J and 3l, the landing gear would remain retractedso long as the air speed of the craft was above the minimum speed. Ifthe speed of the craft fell below the speed necessary to maintaincontacts 35 and 38 connected, the circuit would 'remain completedthrough resistor 31, and-the current through the coil would still be-suicient to maintain the relay energized.

As the craft approaches for a landing it noses downwardly so thatmercury 35 connects contacts 29 and 3| while the speed is decreasedsumciently -v so that bellows 4I contracts connecting contacts 32 and38. In this position (see Fig. 3), coil I1 is shorted out of the circuitand the relay I6 is deenergized, armature I8 returning to its `normalposition so that motor I5 is energized in the opposite `directionthereby driving selector I4 to the extended position, as shown. Ifdesired, a switch maybe added .so .as to break the circuit of the systemafter the landing of the craft.

Various modifications are contemplated and may obviously be resorted toby those skilled in the 'art without departing from the spirit and scopeof the invention, as hereinafter defined by the appended claims, as onlya preferred embodiment thereof has been disclosed.

Therinvention'described herein may be manufactured and used by or forthe Government of the 4United States `of America for Egovernmentalpurposes without the payment of `any royalties -thereon or therefor.

What is claimed is:

1. In van aircraft having retractable ,landing gear and an actuatingsource for controllingsaid gear, an yautomatic control system comprisingmoti-ve means, means operable by said motive means for controlling theoperation of said source, Vrelaymeans foractuating saidmotive means,land'switch means responsive to the .speediand the 1nfclination of theaircraft for controlling the venergization of said relaymeans 2. In 1anaircraft having retractable landing gear, an automatic control systemcomprising mo- ;tivemeans, selector means operable bysaid motive meansfor controlling the position of said gear, a `source of energy for saidmotive means, .relay means connected .between said source `and-saidmotive means for controlling the operation of said motive means, andswitch means responsive tothe speed and the vinclination of the aircraftfor controlling Vthe energization of said relay means.

3. In an aircraft, in combination, retractable landng fgear, motivemeans jfor controlling 'the position of saidlanding gear, a source ofenergy for 'said 'motive means, relay means for controlling the energysupplied by said'source to said motive means, and switch meansresponsive to the speed and the inclination of the aircraft forcontrolling the energization of said relay means.

'-4. The combinationaccording to claim 3, wherein said switch meanscomprises an inclinometer switch responsive to the vinclination of saidaircraft and an air speed switch :responsive to the speed of saidaircraft.

5. In an aircraft .having retractable .landing gear, Yan automaticicontrol ysystem icomprising motivemeans for controlling'the position of.said landing gear, afsourcevof energy, .relay .means 'for controllingthe energy supplied by said sourcel to said motive means, and 'switchmeans -for controlling the .energization of said relay means,s`aidswitch means comprising an inclinometer switch responsive Sto theinclination of said aircraft and an iair :speed "switch responsive tothe speed of said aircraft.

V6. In a system for automatically controllingthe operation of aircraftretractable landing gear, the combination comprising reversible motiveAmeans foricontrolling the `position of said gear, a source ofelectricalenergy, relaymeans for controlling thedirection of energization of saidmotive means from said source, a first switch responsiveto theinclination of the aircraft for controlling the en ergization of saidrelay means, and a second switch responsive to the airspeed of theaircraft for controlling the energization of said relay means, saidswitches being so arranged that actuation of either of them isinsufiicient to energize said relay means but is suicient to maintainsaid relay means energized.

7. In a system for automatically controlling the operation of aircraftretractable landing gear, the combination comprising a source ofelectrical energy, relay means having a coil energizable from saidsource for controlling the position of said gear, an inclinometer switchhaving a plurality of pairs of normally open contacts, one of each ofsaid pairs being connected to one terminal of said source, and anairspeed switch having a movable contact responsive to airspeed andconnected to one end of said coil and a pair of fixed contacts connectedto the other terminal of said source and to the other of one of saidpairs of contacts respectively, the other of another of said pairs ofcontacts being connected to the other terminal of said coil.

8. The combination according to claim 7, wherein said inclinometerswitch has two pairs of normally open contacts arranged so that one ofsaid two pairs of contacts closes when the aircraft is downwardlyinclined beyond a predetermined angle and the other of said two pairs ofcontacts closes when the aircraft is upwardly inclined beyond apredetermined angle.

JAMES H. MILLER.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS

